There is known a technique for displaying, for example, a meter image on a display mounted on a vehicle. For example, Patent Literature 1 discloses a technique for displaying meter images representing the vehicle speed and the engine RPM on one display and displaying a map image between the meter images.
When a plurality of images are displayed on one display, a plurality of image generation devices may generate the respective images. For example, a meter ECU may generate the meter images representing the vehicle speed and the engine RPM, and an ECU of a navigation device may generate the map image.
A video interface mounted on the vehicle may acquire an image generated by an external device, and the acquired image may be displayed on the display together with the above meter images.
An instruction for changing the colors of the plurality of images displayed on the display may be performed, for example, when a user performs an operation of adjusting the brightness of the display, or when an image display mode is changed from a daytime mode to a nighttime mode. Further, for example, a first image generation device and a second image generation device may respectively generate a first image and a second image.
In order to change the colors of the plurality of images displayed on the display, the first image generation device and the second image generation device may respectively change the color of the first image and the color of the second image, and the first image with the color changed and the second image with the color changed may be synthesized.
Further, it is often difficult to transmit a signal representing an instruction for changing color to an external device to change the color in the external device. Thus, when either the first image generation device or the second image generation device (here, the second image generation device) is an external device, the color of the second image may be changed in an image acquisition unit such as a video interface which acquires an image from the external device. Also when the color of the second image is changed in the image acquisition unit, the color of the first image and the color of the second image are changed by the different devices.
When the first image and the second image are synthesized after the change of the colors by the different devices, a timing of changing color is highly likely to differ between a part corresponding to the first image and a part corresponding to the second image in the synthetic image.
Although the first image and the second image are displayed on the same display, the difference in the timing of changing color between the part corresponding to the first image and the part corresponding to the second image disadvantageously gives a sense of incongruity to a user. Similarly, as a matter of course, this problem occurs also when a synthetic image is obtained by synthesizing element images generated by three or more image generation units.